1. Field of the Invention
The present invention relates to a sliding-type magnetic head for magnetooptically recording information on a magneto-optical recording medium in sliding contact therewith.
2. Description of the Relevant Art
One of optical discs for storing, erasing, and retrieving information with a light beam is known as a magneto-optical disc.
As shown in FIG. 1 of the accompanying drawings, a conventional magneto-optical disc 1 comprises a transparent substrate 2, a magneto-optical recording layer 3 in the form of a perpendicularly magnetizable film disposed on the transparent substrate 2 with an SiN protective film 8 interposed therebetween, a reflecting film 4 in the form of a thin metal film such as an aluminum film disposed on the magneto-optical recording layer 3 with another Sin protective film 8 interposed therebetween, and a protective film 5 as of an ultraviolet-curing resin disposed on the reflecting film 4,
Field- and beam-modulating recording processes are known for recording information on magneto-optical discs.
The field-modulating recording process is capable of recording information in an overwrite mode in which a new signal is recorded over an old signal on the magneto-optical disc. The field-modulating recording process will be described below with reference to FIG. 2 of the accompanying drawings. An optical pickup for applying a laser beams 6 is disposed on one side of a magneto-optical disc 1 with a magneto-optical recording layer in the form of a perpendicularly magnetizable film, i.e., on the substrate side of the magneto-optical disc 1, and a magnetic field generator, i.e., a magnetic head 7, is disposed on the other side of the magneto-optical disc 1, i.e., on the protective film side, for movement in synchronism with the laser spot. The direction of the magnetic field generated by the magnetic head 7 is varied by varying the direction of an electric current supplied to the magnetic head 7.
In operation, the magneto-optical disc 1 is rotated about its own center at a predetermined speed.
It is assumed that a magnetic field representing a recording signal is generated in the vicinity of a laser spot 6a on the magneto-optical disc 1. A region 1A of the magneto-optical disc 2, in which recorded information is to be rewritten, is heated to the Curie temperature by the laser spot 6a and hence demagnetized. When the region 1A is moved out of the laser spot 6a on rotation of the magneto-optical disc 1, the temperature of the region 1A drops below the Curie temperature, and the region 1A is magnetized in the direction of the applied magnetic field, thus recording the signal.
The magneto-optical disc 1 is a non-contact recording medium, i.e., the magnetic head 7 is spaced from the magneto-optical disc 1 by a predetermined distance d.sub.0.
The assignee of the present application has developed an ultrasmall-size digital recording and reproducing apparatus for digitally recording information on and reproducing information from an ultrasmall-size magneto-optical disc. This recording and reproducing apparatus employs a field-modulating type magneto-optical recording system and is capable of recording information on a magneto-optical disc in an overwrite mode.
Since the conventional magnetic head 7 is held out of contact with the magneto-optical disc 1 when recording information thereon, the magnetic head 7 is associated with an electromagnetic servo mechanism for causing the magnetic head 7 to follow disc surface displacements that occur due to any inclination of the magneto-optical disc 1, thickness irregularities thereof, etc., when the magneto-optical disc 1 rotates. The presence of the electromagnetic servo mechanism has posed limitations on a recording and reproducing apparatus with respect to efforts to reduce power consumption and apparatus size (particularly apparatus thickness).
Therefore, the assignee of the present application has developed sliding type magnetic heads for magneto-optical recording shown in FIGS. 3A, 3B through FIGS. 6A, 6B.
As shown in FIGS. 3A and 3B, a magnetic head 11 comprises a head element 15 in which a coil 13 is wound around a bobbin 12 having a terminal base 17 having terminals 16 mounted thereon and a flange portion 12a and a ferrite magnetic core 14 of E-shaped configuration in cross section composed of a central magnetic pole core 14a and a side magnetic pole core 14b is disposed so that the central magnetic pole core 14a is inserted into the central aperture of the bobbin 12 and a sheet-shaped sliding portion 18 wound around the head element 15 so as to protrude the top of the central magnetic pole core 14a along the surface of the flange portion 12a. Wire ends of the coils 13 are coupled to the terminals 16, respectively. Reference numeral 19 depicts a head arm made of a resilient material for supporting the magnetic head 11.
Since the sheet-shaped sliding portion 18 is brought in sliding contact with the surface of the magneto-optical disc 1 and the central magnetic pole core 14a is out of direct contact with the disc surface, the magnetic head 11 can be smoothly slid on the surface of the magneto-optical disc 1. Even when the magneto-optical disc 1 has surface irregularities such as bumps or the like, shocks that are imposed upon the magneto-optical disc 1 by the bump or the like are absorbed by the sheet-shaped sliding portion 18 and hence alleviated.
As shown in FIGS. 4A and 4B, a magnetic head 21 comprises a head element 15 in which a coil 13 is wound around a bobbin 12 having terminal bases 17 with terminals 16 implanted thereon and a flange portion 12a and a ferrite magnetic core 14 of E-shaped configuration is mounted on the bobbin 12. Also, the bobbin 12 spaced from the flange portion 12a by a predetermined distance includes at its top a plurality of, for example, eight radially extended portions 22 and spherical sliding portions 23 unitarily formed with the tops of the extended portions 22.
Since the tops of the radially extended portions 22 are brought in sliding contact with the disc surface and the central magnetic pole core 14a is not brought in contact with the disc surface, the magnetic head 21 can be smoothly slid on the surface of the magneto-optical disc 1.
A magnetic head 25 shown in FIG. 5 is a modified example of the above magnetic head 21. As shown in FIG. 5, the four radially extended portions 22 have one or two sliding portions 23 mounted on the tops thereof.
A magnetic head 27 shown in FIGS. 6A and 6B has a circular sliding portion 28 formed on the top of the bobbin 12 spaced from the flange portion 12a. A coil receiving portion 29 incorporates therein a coil spring (not shown) that applies a predetermined load onto the magnetic head 27 to cause the magnetic head 27 to be brought in contact with the disc surface.
As shown in FIG. 7, the magneto-optical disc 1 has a region n in which information can be reliably recorded and reproduced (hereinafter simply referred to as a reliable recording and reproducing region n) extending toward an outer peripheral point A of the recording layer 3 and the protective film 5 has a bump portion 5a formed from the outer peripheral point A to the outermost periphery of the magneto-optical disc 1.
The above-mentioned magnetic head 11, 21, 25 or 27 has the sliding portions 18, 23 or 28 disposed about the central magnetic pole core 14a in the multiple angle directions (360.degree.) so that, when the central magnetic pole core 14a is brought about to the point A, the sliding portion 18, 23 or 28 hits the bump portion 5a formed on the outermost periphery of the magneto-optical disc 1. Thus, the bump portion 5a exerts a bad influence upon the transport of the magnetic head 11, 21, 25 or 27 to cause the optical pickup system to be defocused and the head element to have a spacing loss, etc.
To avoid the sliding portion from hitting the bump portion 5a, it is unavoidable that an actual recording and reproducing region must be made narrower than the aforesaid reliable recording and reproducing region n.